Various sensors, including load cells, accelerometers, pressure sensors, temperature sensors and others, may utilize a miniature mechanical resonator as a transducer element. Some such sensors may be designed such that the physical quality to be measured results in axial tension or compression being applied to a vibrating beam to alter its resonant frequency. Some such sensors may be designed such that the physical quality to be measured results in axial tension or compression being applied to a vibrating beam to alter its resonant frequency. Temperature sensors may be designed such that their resonant frequency is altered based on their temperature-sensitive material properties. Various miniature electromechanical filters may also utilize one or more miniature mechanical resonators as filtering elements.
Prior art teachings indicate that the performance of such mechanical resonators is degraded if there is a transfer or loss of energy between the vibrating beam and an external supporting structure, for example due to reaction forces where the beam element is coupled to a supporting structure. Such transfer or loss of energy can lower the Q of the vibrating beam, and/or cause an undesirable unpredictable change in the resonant frequency.
One prior art method used to limit energy transfer in miniature vibrating beam mechanical resonators is the utilization of multiple resonant beams located proximate to one another and vibrating out of phase, such that their reaction forces cancel one another proximate to the end of the beams. Examples of such multiple beam elements are disclosed in U.S. Pat. Nos. 4,215,570; 4,372,173; 4,415,827; 4,901,586; 5,331,242; and 5,367,217, each of which is incorporated herein by reference in its entirety. However, for such known configurations, it has been observed that the effectiveness of this technique will be degraded when the resonant frequencies of the individual beams vary from one another, for example due to fabrication variations. In addition, such configurations are sensitive to frequency shifts and/or non-linearities due to beam distortion arising from non-ideal mounting conditions, misaligned force application, or the like.
Another prior art method used to limit energy transfer in miniature vibrating beam elements is the utilization of a resonant beam (or beams) that is (are) coupled to one or more counterbalances configured such that the reaction forces of the vibrating beam and the counterbalances cancel one another. Examples of such elements are disclosed in U.S. Pat. Nos. 5,435,195; 5,450,762; and 6,269,698, each of which is incorporated herein by reference in its entirety. The '762 and '698 patents emphasize configurations wherein the vibrating beam element is fabricated as a generally planar element, and the resonant beam vibrates in the plane of the element. The '762 and '698 patents teach a counterbalancing technique wherein either the residual forces, or moments, can be reduced at the beam supports, each at the expense of increase in the other. Therefore, the allocation of residual forces and moments are determined for each particular application. In any case, a reduced but still undesirable energy transfer may occur due to the unbalanced residual forces or moments. In addition, counterbalanced designs such as those disclosed the '762, '698, and '195 patents may still be sensitive to non-ideal mounting conditions (e.g., non-planar mounting or distortion). The '195 patent emphasizes configurations wherein the vibrating beam element is fabricated as a generally planar element, and a single beam, and a counter balance arrangement that is symmetrical around the beam axis, vibrate along a direction that is perpendicular to the plane of the element. The '195 patent discloses various spring configurations that may be incorporated with the suspension of the vibrating beam element in order to reduce its sensitivity to non-ideal mounting conditions. However, such spring configurations may introduce unwanted spurious frequencies, frequency nonlinearities, stress concentrations, size restrictions, and/or additional resonances, any of which may be undesirable in various applications. In addition, in the case of force sensing vibrating beam elements, such spring configurations generally reduce the sensitivity of the resonant frequency to applied external forces, which is particularly detrimental to force sensing applications.
U.S. Pat. No. 6,600,252, which is incorporated herein by reference in its entirety, describes miniature mechanical resonators that are integrated into micro-electromechanical devices with associated circuitry, and employed as electromechanical frequency filtering elements. The '252 patent teaches relatively crude means of supporting the miniature mechanical resonators, including the use of dimples that extend between a support structure and nodal points of the mechanical resonators along a direction normal to the mechanical resonator. Such support means may be relatively impractical to fabricate and/or less effective than is desirable in terms of energy isolation.
A configuration for a miniature mechanical resonator that can provide lower energy transfer to an external supporting structure and/or provide lower sensitivity to non-ideal mounting conditions or distortion, while avoiding one or more of the previously described deficiencies or other limitations inherent in the prior art, would be desirable.